Blender not rendering specified dimensions
The stretched height comes from you having an 3:2 aspect ratio.

You would normally only want to adjust the aspect ratio when rendering video that is intended for older tv's with non-square pixels.

The reason you are seeing the distortion is that the uv image editor displays images in 1:1 aspect by default, you can adjust this to match your render settings in the Display panel of the UV/Image Editors properties region N.